Check valve designs that are arranged in the standard "T" configuration with the input and output positioned on opposing ends of the end block of the intensifier piston cylinder, are subjected to cyclic stress and fatigue resulting from the full range of applied stress that occurs during each intensifier piston stroke. With each piston stroke, the movable check valve piston hits the valve seat with considerable force, resulting in the deterioration of the common seating surfaces. In efforts to eliminate or reduce the incidence of valve failure, known valve designs have incorporated features such as easily repairable or easily replaceable valve pistons and valve seating surfaces, such as described in U.S. Pat. No. 4,371,001. Additionally, some known check valve designs reduce the degree of cyclic stress by arranging the valves coaxially, or by securing the valve assembly into the end of the intensifier cylinder as described in U.S. Pat. No. 4,026,322; U.S. Pat. No. 4,412,792; and U.S. Pat. No. 4,862,911. These check valves are designed for use with only pure water/polymer solutions.
A number of water jet pump systems are equipped with an absolute prefiltration process capable of removing particles smaller than 5 microns, which ensures that no large particles are encountered by the check valves. U.S. Pat. No. 4,908,154 discusses the need for incorporating two prefiltration steps to ensure that large particles do not contact the processing system.
Commercially available check valve designs are not always suitable for functioning in an abrasive slurry environment at operating pressures up to 2,873,000 N/m.sup.2 (60,000 psi), at production-conducive throughput rates (greater than 0.5 gpm), because these valves are designed primarily for a water/polymer environment. The mode of failure of commercial valves is most commonly an erosion of the ball and corresponding seating surface, caused by the inability of the valve to seat securely, due to pigment particles becoming lodged between the ball-seat interface.
Valve seating designs incorporating a chamfer on the inside of the seat, with or without an elastomer O-ring, allow for faster build-up of particles between the bail-seat interface which results in an increase in the frequency of erosion failures. Elastomer O-rings, used in known valve designs to improve seating, fail due to the direct impingement by the abrasive stream, or due to the inability of the elastomer to withstand the solvent absorption/decompression, which occurs in a high pressure environment.
The onset of the erosion of the check valve seating surfaces could be slightly retarded by using hard ceramic materials, such as partially stabilized zirconia as part of the seating surface. However, this approach is not sufficiently erosion-resistant as the same type of erosion pattern that occurs on seats having softer metal material would eventually occur on the ceramic seat. The valve in U.S. Pat. No. 5,110,463 incorporates a hard ceramic seating surface.